Radiation exposure apparatus comprising a gas flushing system

ABSTRACT

An exposure apparatus is provided with a radiation source, a patterning structure, a projection system, a substrate, and a gas flushing system for introducing flushing gas in an area between the projection system and the substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional application60/633,727 , filed 7 Dec. 2004, which is hereby incorporated in itsentirety by reference.

FIELD OF THE INVENTION

This invention relates to a radiation exposure apparatus, e.g. alithographic projection apparatus, and more particularly to an exposureapparatus including a gas flushing system. Also, this invention relatesto methods concerning exposing a substrate to radiation.

BACKGROUND

The use of resist-type materials for color filters in the production ofimage sensors, such as Charged Coupled Device (CCD) image sensors andComplimentary Metal Oxide Semiconductor (CMOS) image sensors, raisescontamination concerns. For instance, volatile components in the resistsmay cause substantial out-gassing during exposure to radiation, e.g.during exposure to radiation in a lithographic image sensormanufacturing process. The out-gassing may lead to contamination anddamage of the projection lens or the surrounding area, which in turn mayrequire increased maintenance to clean the lens or even replacement ofthe lens or surrounding parts. Objectives of the present inventioninclude providing methods and apparatus addressing out-gassing concerns.

Lithography systems employing gas purgehoods are mentioned in EP 1098226and US 2004-0212791.

SUMMARY OF THE INVENTION

In one embodiment, the present invention provides a method ofmanufacturing a device, e.g. an image sensor, comprising:

-   (a) providing a beam of radiation;-   (b) patterning the beam of radiation;-   (c) projecting the patterned beam of radiation via a projection    system onto a target portion of a substrate comprising a    radiation-sensitive layer; and-   (d) flowing a flushing gas from a first gas outlet positioned    outside the circumference of said target portion to a space between    said projection system and said substrate;    wherein at least part of said flushing gas flows towards said target    portion.

Also, the present invention provides a method comprising:

-   (a) providing a beam of radiation;-   (b) patterning the beam of radiation;-   (c) projecting the patterned beam of radiation via a projection    system onto a target portion of a substrate comprising one or more    color filter layers; and-   (d) extracting gases emanating from said target portion during    exposure of said target portion to said patterned beam of radiation    by providing an air flow in the space between said target portion    and said projection system.

In one embodiment, the present invention provides a lithographicprojection apparatus comprising:

-   (a) a radiation system constructed and arranged to supply a    projection beam of radiation;-   (b) a support structure constructed and arranged to support a    patterning structure, the patterning structure being constructed and    arranged to pattern the projection beam according to a desired    pattern;-   (c) a substrate support constructed and arranged to support a    substrate;-   (d) a projection system constructed and arranged to project the    patterned beam onto a target portion of the substrate; and-   (e) a gas flushing system comprising radial gas flow outlets, said    gas flushing system being constructed and arranged to generate a    radial gas flow through said radial gas flow outlets in an    intermediate space defined between said gas flushing system and said    substrate, with at least part of said radial gas flow having a    radial velocity directed towards the area between the substrate and    the projection system.

In another embodiment, the present invention provides a lithographicprojection apparatus comprising:

a radiation system constructed and arranged to supply a projection beamof radiation;

a support structure constructed and arranged to support a patterningstructure, the patterning structure constructed and arranged to patternthe projection beam according to a desired pattern;

a substrate support constructed and arranged to support a substrate;

a projection system constructed and arranged to project the patternedbeam onto a target portion of the substrate; and

a gas flushing system that creates a laminar flow in a first directionacross said substrate, and further creates a secondary flow havingportions thereof traveling in at least one direction substantiallydifferent from said first direction, said secondary flow being generallybelow said laminar flow, the gas flushing system further creating a gasflow in between said laminar flow and said secondary flow designed toremove gas introduced by at least said secondary flow.

In addition, the present invention provides a lithographic projectionapparatus comprising:

a radiation system constructed and arranged to supply a projection beamof radiation;

a support structure constructed and arranged to support a patterningstructure, the patterning structure constructed and arranged to patternthe projection beam according to a desired pattern;

a substrate support constructed and arranged to support a substrate;

a projection system constructed and arranged to project the patternedbeam onto a target portion of the substrate; and

a gas flushing system that includes a first outlet that generates alaminar flow in a first direction, generally parallel to an uppersurface of said substrate, and a second outlet that directs gas in adirection towards said target portion.

Also, the present invention provides a process comprising exposing aportion of a substrate having one or more color filter resist layers toradiation and extracting gases emanating from the portion being exposedwith a gas flushing system.

Furthermore, the present invention provides an apparatus for themanufacturing of image sensors, wherein the apparatus comprises a gasflushing system for removal of gases emanating from, e.g., one or morecolor filter resist layers.

Additional objects, advantages and features of the present invention areset forth in this specification, and in part will become apparent tothose skilled in the art on examination of the following, or may belearned by practice of the invention. The inventions disclosed in thisapplication are not limited to any particular set of or combination ofobjects, advantages and features. It is contemplated that variouscombinations of the stated objects, advantages and features make up theinventions disclosed in this application.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 represents an exposure apparatus according to an embodiment ofthe present invention.

FIG. 2 represents a cross-sectional front view of an embodiment of a gasflushing system according to the present invention.

FIGS. 3 a-c represent several embodiments of a bottom view of a gasflushing system and final lens element of a projection system accordingto the present invention.

DETAILED DESCRIPTION

The term “patterning structure” used herein should be broadlyinterpreted as referring to structure that may be used to endow anincoming radiation beam with a patterned cross-section, corresponding toa pattern that is to be created in a target portion of the substrate;the term “light valve” may also be used in this context. Generally, thesaid pattern will correspond to a particular functional layer in adevice being created in the target portion, such as an integratedcircuit or other device (see below). Examples of such patterningstructure include:

A mask. The concept of a mask is well known in lithography, and itincludes mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. Placementof such a mask in the radiation beam causes selective transmission (inthe case of a transmissive mask) or reflection (in the case of areflective mask) of the radiation impinging on the mask, according tothe pattern on the mask. In the case of a mask, the support structurewill generally be a mask table, which ensures that the mask may be heldat a desired position in the incoming radiation beam, and that it may bemoved relative to the beam if so desired;

An array of individually controllable elements, for instance aprogrammable mirror array or a programmable LCD array. One example of aprogrammable mirror array is a matrix-addressable surface having aviscoelastic control layer and a reflective surface. The basic principlebehind such an apparatus is that (for example) addressed areas of thereflective surface reflect incident light as diffracted light, whereasunaddressed areas reflect incident light as undiffracted light. Using anappropriate filter, the undiffracted light may be filtered out of thereflected beam, leaving only the diffracted light behind; in thismanner, the beam becomes patterned according to the addressing patternof the matrix-addressable surface. An alternative embodiment of aprogrammable mirror array employs a matrix arrangement of tiny mirrors,each of which may be individually tilted about an axis by applying asuitable localized electric field, or by employing piezoelectricactuation means. Once again, the mirrors are matrix-addressable, suchthat addressed mirrors may reflect an incoming radiation beam in adifferent direction to unaddressed mirrors; in this manner, thereflected beam is patterned according to the addressing pattern of thematrix-addressable mirrors. The matrix addressing may be performed usingsuitable electronic devices. In both of the situations describedhereabove, the patterning structure may comprise one or moreprogrammable mirror arrays. More information on mirror arrays as herereferred to may be gleaned, for example, from U.S. Pat. Nos. 5,296,891and 5,523,193, and PCT patent applications WO 98/38597 and WO 98/33096,which are incorporated herein by reference. In the case of aprogrammable mirror array, the said support structure may be embodied asa frame or table, for example, which may be fixed or movable asrequired. A programmable LCD array. An example of a programmable LCDarray is given in, for instance, U.S. Pat. No. 5,229,872, which isincorporated herein by reference. As above, the support structure inthis case may be embodied as a frame or table, for example, which may befixed or movable as required.

For purposes of simplicity, the rest of this text may, at certainlocations, specifically direct itself to examples involving a mask andmask table; however, the general principles discussed in such instancesshould be seen in the broader context of the patterning structure ashereabove set forth.

For the sake of simplicity, the projection system may hereinafter bereferred to as the “lens”; however, this term should be broadlyinterpreted as encompassing various types of projection system,including refractive optics, reflective optics, and catadioptricsystems, for example. The radiation system may also include componentsoperating according to any of these design types for directing, shapingor controlling the projection beam of radiation, and such components mayalso be referred to below, collectively or singularly, as a “lens”.Further, the lithographic apparatus may be of a type having two or moresubstrate tables (and/or two or more mask tables). In such “multiplestage” devices the additional tables may be used in parallel, orpreparatory steps may be carried out on one or more tables while one ormore other tables are being used for exposures. Dual stage lithographicapparatus are described, for example, in U.S. Pat. No. 5,969,441 and WO98/40791, both incorporated herein by reference.

The term “outlet” as used herein may also be considered or termed as anoutlet port. Similarly, the term “inlet” as used herein may also beconsidered or termed as an inlet port. It should be understood that theterms outlet, outlet port, inlet and inlet port broadly refer to astructure through which a gas or substance flows.

In a manufacturing process using a lithographic projection apparatus, apattern (e.g. in a mask) may be imaged onto a substrate that is at leastpartially covered by a layer of radiation-sensitive material (resist).Prior to this imaging step, the substrate may undergo variousprocedures, such as priming, resist coating and a soft bake. Afterexposure, the substrate may be subjected to other procedures, such as apost-exposure bake (PEB), development, a hard bake andmeasurement/inspection of the imaged features. This array of proceduresis used as a basis to pattern an individual layer of a device, e.g. animage sensor, a flat panel display, or an integrated ciruit. Such apatterned layer may then undergo various processes such as etching,ion-implantation (doping), metallization, oxidation, chemo-mechanicalpolishing, etc., all intended to finish off an individual layer. Ifseveral layers are required, then the whole procedure, or a variantthereof, may be repeated for each new layer. Eventually, an array ofdevices will be present on the substrate (wafer). These devices are thenseparated from one another by a technique such as dicing or sawing,whence the individual devices may be mounted on a carrier, connected topins, etc. Further information regarding such processes may be obtained,for example, from the book “Microchip Fabrication: A Practical Guide toSemiconductor Processing”, Third Edition, by Peter van Zant, McGraw HillPublishing Co., 1997, ISBN 0-07-067250-4, incorporated herein byreference.

FIG. 1 schematically depicts a lithographic apparatus according to aparticular embodiment of the invention. The apparatus comprises:

an illumination system (illuminator) IL for providing a projection beamPB of radiation (e.g. UV radiation or DUV radiation).

a first support structure (e.g. a mask table) MT for supportingpatterning means (e.g. a mask) MA and connected to first positioningmeans PM for accurately positioning the patterning means with respect toprojection system PL;

a substrate table (e.g. a wafer table) WT for holding a substrate (e.g.a resist-coated wafer) W and connected to second positioning means PWfor accurately positioning the substrate with respect to projectionsystem PL;

a projection system (e.g. a refractive projection lens) PL for imaging apattern imparted to the projection beam PB by patterning means MA onto atarget portion C (e.g. comprising one or more dies) of the substrate W;and

a gas flushing system GF. As depicted here, the gas flushing system issecured via a frame. However, the flushing system GF may be secured inany suitable manner.

As here depicted, the apparatus is of a transmissive type (e.g.employing a transmissive mask). Alternatively, the apparatus may be of areflective type (e.g. employing a programmable mirror array of a type asreferred to above).

The illuminator IL receives a beam of radiation from a radiation sourceSO. In one embodiment, the radiation source supplies radiation of atleast 126 nm, e.g. at least 157 nm or at least 193 nm, for instance inthe range of 193-435 nm or, such as 193 nm, 248 nm, or 365 nm, or in therange of 220-435 nm. The source and the lithographic apparatus may beseparate entities, for example when the source is an excimer laser. Insuch cases, the source is not considered to form part of thelithographic apparatus and the radiation beam is passed from the sourceSO to the illuminator IL with the aid of a beam delivery system BDcomprising for example suitable directing mirrors and/or a beamexpander. In other cases the source may be integral part of theapparatus, for example when the source is a mercury lamp. The source SOand the illuminator IL, together with the beam delivery system BD ifrequired, may be referred to as a radiation system.

The illuminator IL may comprise adjusting means AM for adjusting theangular intensity distribution of the beam. Generally, at least theouter and/or inner radial extent (commonly referred to as σ-outer andσ-inner, respectively) of the intensity distribution in a pupil plane ofthe illuminator may be adjusted. In addition, the illuminator ILgenerally comprises various other components, such as an integrator INand a condenser CO. The illuminator provides a conditioned beam ofradiation, referred to as the projection beam PB, having a desireduniformity and intensity distribution in its cross-section.

The projection beam PB is incident on the mask MA, which is held on themask table MT. Having traversed the mask MA, the projection beam PBpasses through the lens PL, which focuses the beam onto a target portionC of the substrate W. With the aid of the second positioning means PWand position sensor IF (e.g. an interferometric device), the substratetable WT may be moved accurately, e.g. so as to position differenttarget portions C in the path of the beam PB. Similarly, the firstpositioning means PM and another position sensor (which is notexplicitly depicted in FIG. 1) may be used to accurately position themask MA with respect to the path of the beam PB, e.g. after mechanicalretrieval from a mask library, or during a scan. In general, movement ofthe object tables MT and WT will be realized with the aid of along-stroke module (coarse positioning) and a short-stroke module (finepositioning), which form part of the positioning means PM and PW.However, in the case of a stepper (as opposed to a scanner) the masktable MT may be connected to a short stroke actuator only, or may befixed. Mask MA and substrate W may be aligned using mask alignment marksM1, M2 and substrate alignment marks P1, P2.

The depicted apparatus may be used in the following preferred modes:

1. In step mode, the mask table MT and the substrate table WT are keptessentially stationary, while an entire pattern imparted to theprojection beam is projected onto a target portion C in one go (i.e. asingle static exposure). The substrate table WT is then shifted in the Xand/or Y direction so that a different target portion C may be exposed.In step mode, the maximum size of the exposure field limits the size ofthe target portion C imaged in a single static exposure.

2. In scan mode, the mask table MT and the substrate table WT arescanned synchronously while a pattern imparted to the projection beam isprojected onto a target portion C (i.e. a single dynamic exposure). Thevelocity and direction of the substrate table WT relative to the masktable MT is determined by the (de-)magnification and image reversalcharacteristics of the projection system PL. In scan mode, the maximumsize of the exposure field limits the width (in the non-scanningdirection) of the target portion in a single dynamic exposure, whereasthe length of the scanning motion determines the height (in the scanningdirection) of the target portion.

3. In another mode, the mask table MT is kept essentially stationaryholding a programmable patterning means, and the substrate table WT ismoved or scanned while a pattern imparted to the projection beam isprojected onto a target portion C. In this mode, generally a pulsedradiation source is employed and the programmable patterning means isupdated as required after each movement of the substrate table WT or inbetween successive radiation pulses during a scan. This mode ofoperation may be readily applied to maskless lithography that utilizesprogrammable patterning means, such as a programmable mirror array of atype as referred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

FIG. 2 represents an embodiment of the gas flushing system GF in moredetail. Gas flushing system GF comprises a first gas outlet GO-1 and asecond gas outlet GO-2. In the depicted embodiment, GO-1 and GO-2 areconnected via gas supply channel GC to a flushing gas supply (not shown)comprising a gas source (not shown) and optionally a flow regulator (notshown). As depicted in FIG. 2, i.e. by being directly connected via gassupply channel GC, both GO-1 and GO-2 receive gas from a single source.However, GO-1 and GO-2 may also each have a separate gas supply channel,whereby the separate gas supply channels may receive gas from the samesource or each may receive gas from a separate gas source. In oneembodiment, at least gas outlet GO-1 receives an oxygen containing gas.In one embodiment, at least 1 mole % of the gas supplied to GO-1 isoxygen, for instance at least 5 mole %, at least 10 mole %, for instance10-50 mole % or 10-30 mole %. In one embodiment, the gas supplied toGO-1 is air. In one embodiment, GO-2 receives an inert gas, for instancenitrogen, argon, helium, xenon, or mixtures thereof. In otherembodiments, both GO-1 and GO-2 receive an inert gas or an oxygencontaining gas.

In one embodiment, as indicated in FIG. 2, at least part of the gasexiting GO-1 is directed towards the target portion of substrate W thatis being exposed to the radiation exiting the projection system PL(i.e., at least part of the gas exiting GO-1 is directed towards thesubstrate and angled towards the area being exposed to the radiation).In one embodiment, essentially all gas exiting GO-1 is directed towardsthe target portion of substrate W that is being exposed to the radiationexiting the projection system PL (only the bottom section of projectionsystem PL is shown).

In one embodiment, the gas flow from outlet GO-1 is adjusted such that,at the used substrate table (or substrate support) velocity, thevelocity of the radial gas flow, at every location in the space betweenthe gas flushing system and the substrate is higher than zero anddirected inwards, i.e. towards the area between the substrate and theprojection system. The radial gas flow velocity is the vectorial sum ofgas flow speed created at the outlet(s) GO-1 and the substrate tablevelocity. The term “substrate table velocity” includes, e.g., thesubstrate table (or substrate support) scanning velocity of astep-and-scan type lithographic projection apparatus, as well as, in thecase of a step-and-repeat type lithographic projection apparatus, thevelocity of the wafer table between subsequent exposures.

Furthermore, remaining with FIG. 2, gas flushing system GF comprises agas inlet GI for extracting gas from the space between the targetportion being exposed and the projection system. Gas inlet GI isconnected via channel GIC to a gas extraction system (not shown), whichmay include a vacuum pump and/or a fan for facilitating the removal ofthe gas. Also, the gas extraction system may include a flow regulator.

In one embodiment, the gas flushing system comprises one or moresensors, e.g. for determining the amount and/or type of harmful gasesentering the area between the substrate and the projection system. Theone or more sensors may be used to adjust the composition and/or rate ofthe flushing gas, e.g. relative to the amount and/or type of harmfulgases entering the area between the substrate and the projection system.

Referring to FIG. 3, several embodiments for providing gas outlet GO-2are shown. In the embodiment of FIG. 3 a, the gas flushing system GF hasa circular construction and, along its inner circumference, only part ofthe gas flushing system is provided with a gas outlet section GO-2. InFIG. 3 b, gas outlet ports GO-2 are provided all along the innercircumference of the gas flushing system, and in FIG. 3 c the gasflushing system GF is provided with opposing gas outlet ports. In oneembodiment, gas outlet port(s) GO-2 provide a laminar flow substantiallyparallel to the surface of the substrate and/or the surface of thebottom lens of projection system PL.

While not limited thereto, the gas flushing system is useful inprocesses where there is a risk of harmful gases evaporating from asubstrate during exposure to radiation. Such gases may, for instance,damage the projection system or surrounding parts, which may in turnrequire increased maintenance and/or shorten the lifetime of theprojection system or surrounding parts. The gas flushing system of thepresent invention is helpful in preventing such damage by substantiallypreventing harmful gases from reaching the projection system orsurrounding parts. Substrates that are prone to releasing gases are, forinstance, substrates coated with one or more resist layers.Particularly, substrates coated with resist layers for one or more colorfilter layers may be susceptible to releasing gases. Substrates coatedwith resist layers for one or more color filter layers may be used inthe manufacturing of image sensors, for instance image sensors useful incameras (e.g. photocameras or videocameras).

Having described specific embodiments of the present invention, it willbe understood that many modifications thereof will readily appear or maybe suggested to those skilled in the art, and it is intended thereforethat this invention is limited only by the spirit and scope of thefollowing claims.

1. A method of manufacturing a device comprising: providing a beam ofradiation; patterning the beam of radiation; projecting the patternedbeam of radiation via a projection system onto a target portion of asubstrate comprising a radiation-sensitive layer; and flowing a flushinggas from a first gas outlet positioned outside a circumference of saidtarget portion to a space between said projection system and saidsubstrate, wherein, during said projecting, at least part of saidflushing gas flows towards said target portion.
 2. The method accordingto claim 1, further comprising a gas inlet positioned outside thecircumference of said target portion and in between said projectionsystem and said first gas outlet, said gas inlet being constructed andarranged to extract gas from the area between said target portion andsaid projection system.
 3. The method according to claim 1, furthercomprising flowing a second flushing gas from a second outlet portconstructed and arranged to generate a substantially laminar gas flow ofsaid second flushing gas across at least part of said patterned beambetween a last lens of the projection system and said first outlet port.4. The method according to claim 2, further comprising flowing a secondflushing gas from a second outlet port constructed and arranged togenerate a substantially laminar gas flow of said second flushing gasacross at least part of said patterned beam between a last lens of theprojection system and said first outlet port, wherein said gas inlet ispositioned between said first gas outlet and said second gas outlet. 5.The method according to claims 1, wherein said flushing gas comprises atleast 1 mole % oxygen.
 6. The method of claim 5, wherein said flushinggas is air.
 7. The method according to claim 1, wherein said first gasoutlet is a radial gas flow outlet.
 8. The method according to claim 1,wherein said first gas outlet, said second gas outlet, and said gasinlet are all provided in the same radial structure.
 9. The methodaccording to claim 9, wherein said wavelength is in the range of 220nm-435 nm.
 10. The method according to claim 1, wherein said substratecomprises one or more layers required for the manufacturing of colorfilters.
 11. An image sensor obtained by the method according toclaim
 1. 12. A camera comprising the image sensor of claim
 11. 13. Themethod of claim 1, wherein said device is an image sensor.
 14. A methodcomprising: providing a beam of radiation; patterning the beam ofradiation; projecting the patterned beam of radiation via a projectionsystem onto a target portion of a substrate comprising one or more colorfilter layers; and extracting gases emanating from said target portionduring said projecting by providing an air flow in the space betweensaid target portion and said projection system.
 15. A lithographicprojection apparatus comprising: a radiation system constructed andarranged to supply a projection beam of radiation; a support structureconstructed and arranged to support a patterning structure, thepatterning structure being constructed and arranged to pattern theprojection beam according to a desired pattern; a substrate supportconstructed and arranged to support a substrate; a projection systemconstructed and arranged to project the patterned beam onto a targetportion of the substrate; and a gas flushing system comprising a gasoutlet, said gas outlet being constructed and arranged to direct atleast part of the gas exiting said gas outlet towards said targetportion.
 16. The apparatus of claim 15, wherein said radiationprojection beam of radiation has a wavelength in the range of 220-435nm.
 17. The apparatus according to claim 15, wherein said gas outlet isconnected to a gas source comprising a gas having an oxygen content ofat least 1 mole %.
 18. The apparatus according to claim 15, wherein saidgas flushing system further comprises an outlet port constructed andarranged to generate a substantially laminar gas flow across at leastpart of said projection beam between a last lens of the projectionsystem and said substrate, said laminar gas flow being substantiallyparallel to said target portion.
 19. The apparatus according to claim15, wherein said apparatus is designed to operate in step mode.
 20. Aprocess comprising exposing a substrate to radiation with the apparatusof claim 15.